The HOB filter is a topfin30. It has a fairly large amount of space and is big enough to easily filter my freshwater 40g tank (which is where it is right now. I'm upgrading to a canister with higher filtration and the such from a friend for $30.00 but I need to get some internal pieces so he can show me how to clean and do maintenance on it before I hook it up to the tank) I'd say it's about 1 1/2"X3-4"X4-6" (just estimating space) and is in decent condition. So could you tell me all the things I could do with that size mini refugium? The light part is a little uncertain